1. Field of the Invention
The present invention relates to an image inspection device, an image inspection system, and an image inspection method.
2. Description of the Related Art
Conventionally, inspection of printed sheets is performed by hand; however, a device that performs inspection of printed sheets as post-processing of offset printing has been used in recent years. Such an inspection device first generates a reference master image by reading a non-defective image selected by hand from among read images of printed sheets. Then, the inspection device compares a portion of the generated master image and corresponding portions of read images of printed sheets to be inspected, and determines whether the printed sheets have any defects on the basis of the degree of difference from the portion of the master image.
However, plateless printers such as electrophotographic printers, which have been in widespread use in recent years, are suited especially for printing a few copies, and it is often the case that print content differs from page to page, for example, as in the case of variable data printing; therefore, generating a master image from printed sheets and using the master image to compare like an offset printing press is inefficient. To cope with this problem, a master image can be generated from print data. This makes it possible to efficiently handle variable data printing (for example, see Japanese National Publication of International Patent Application No. 2002-531015).
Meanwhile, in an image forming apparatus, even in the case of copies output on the basis of the same image, the copies may vary in density due to aged deterioration of an image formation engine that supplies developer to sheets. For example, in the case of an image forming apparatus that adopts the above-described electrophotographic system, the density may decrease due to deterioration of a light source that exposes a photoreceptor to light or deterioration of developing bias used in development of an electrostatic latent image, etc.
To cope with such issues, there may be used a method to print predetermined density patterns of color patches and correct the density of image information input to an engine in accordance with a read result of respective densities of the printed color patches (for example, see Japanese Patent Application Laid-open No. H8-289149).
A master image as described above is preferably generated on the basis of an image input to an engine to reduce the influence caused by image processing as much as possible. On the other hand, when the density of an image input to an engine is corrected using the technology disclosed in Japanese Patent Application Laid-open No. H8-289149, a master image is generated on the basis of an image reflected with a result of the correction.
The above-described correction of an image input to an engine is performed to keep the density of an image generated on a sheet by supply of developer from the engine constant. On the other hand, when a master image is generated on the basis of an image reflected with a result of the density correction, the density of a generated master image varies depending on the correction, and this density variation causes a difference in density between a read image obtained by reading an output sheet and the master image. As a result, even if the image has no defect, the image may be determined to be defective due to the density variation. Incidentally, such a problem may arise in image formation and output on sheets as well as recording media in general, such as films.
In view of the above, there is a need to enable generation of a master image corresponding to density correction of an image to be formed and output in a system that inspects a result of image formation and output by comparing a read image obtained by reading a sheet and an image for inspection.